This invention relates to a process for converting copper phthalocyanine to pigmentary form, and particularly to an improved process which produces pigmentary copper phthalocyanine characterized by superior tinctorial properties.
Copper phthalocyanines are well known in the art as pigments in a wide variety of applications. Like many other compounds useful as pigments, copper phthalocyanines obtained directly from most conventional syntheses cannot be directly used in pigmentary application because of particle size, crystal habit, texture or other factors which contribute to inadequate tinctorial properties.
Many processes are known in the art for converting crude copper phthalocyanine to pigmentary form. The well known acid pasting procedure whereby the unconditioned or crude copper phthalocyanine is dissolved wholly or partly in concentrated sulfuric acid and the solution drowned in water or an aqueous solution provides a relatively simple means for reduction of the particle size of the crude copper phthalocyanine. However, the use of concentrated mineral acid represents a hazard to personnel, equipment and entails the use of large volumes of reagents and costly equipment. Furthermore, pollution problems can arise in disposing of large volumes of the acid wastes from such processes.
Another technique, known in the art as "solvent milling", involves the grinding of crude phthalocyanines in the presence of certain volatile organic liquids. This general procedure is subject to the disadvantages that the use of rather substantial quantities of relatively expensive organic solvents involves inherent fire and explosion hazards, solvent recovery costs, solvent losses and water pollution problems.
Still another technique, especially applicable to highly chlorinated copper phthalocyanines, involves heating the copper phthalocyanine in an aqueous medium at or above 90.degree. C., preferably between 100.degree. and 300.degree. C., while, advantageously, agitating the mixture. This procedure results in soft, readily dispersible chlorinated copper phthalocyanine, and is effective as a means of breaking up agglomerates of crude chlorinated copper phthalocyanines which are obtained in a finely divided form but which on drying undergo increments in grain size and harden. Such a procedure is ineffective when applied to crude copper phthalocyanines, the particle size of which is relatively large. Even in the case where dry-milled copper phthalocyanine is employed, the tinctorial properties of the resulting pigmentary copper phthalocyanine are not adequate for many high quality pigmentary applications.
In an attempt to overcome the disadvantages of the procedures described above, procedures known as "aqueous milling" were developed. One aqueous milling procedure described in Santimauro et al. U.S. Pat. No. 3,758,321 involves grinding crude unconditioned phthalocyanine compound suspended in a liquid grinding medium comprising water and a liquid water-immiscible volatile organic solvent. The water is present in an amount which is at least 60% by weight of the grinding medium and the organic solvent is in an amount from 15 to 30 parts by weight for each part by weight of the crude phthalocyanine compound. Another aqueous milling procedure described in Minnich et al. U.S. Pat. No. 3,017,414 involves dry milling crude phthalocyanine pigment, contacting the dry-milled phthalocyanine with an organic liquid in water emulsion, and recovering the pigmentary copper phthalocyanine, e.g., via steam distillation. The organic liquid used is selected from nitrobenzene, benzonitrile, unsubstituted aromatic hydrocarbons, chlorinated aromatic hydrocarbons, and chlorinated aliphatic hydrocarbons, boiling between about 100.degree. and 250.degree. C.
Although the aqueous milling procedures described above eliminate many of the disadvantages inherent to other art processes, the tinctorial quality of the copper phthalocyanine pigment so produced, though adequate for many applications, is insufficient for particularly high quality pigmentary applications.
This invention provides for an improved aqueous milling process which, like prior aqueous milling processes, eliminates many of the disadvantages of other art processes and, unlike prior aqueous milling processes, produces a pigmentary copper phthalocyanine having superior tinctorial properties.